A golf swing is composed of a sequence of swing actions starting from an address, a back swing, a top swing, a down swing which leads to an impact and then through a follow-through, coming to a finish. During this series of swing actions from address to finish, the club head moves in a circular path. By making a swing so that the lowest point of the circular path is the ball position, it becomes possible to drive the ball accurately toward a target. A plane which contains the circular path made by the club head when such a swing is made is called swing plane. If the club head travels out of the swing plane during the swing, the ball is likely to make slice rotation or hook rotation.
Therefore, in order to stabilize shots, it is necessary to master a proper swing path along the swing plane. However, since the golfer cannot see his swing path by himself, it is not easy to master a proper swing path. Especially, there is a major tendency in many beginners that their swing often causes the ball to make slice rotation. One reason for this is that people only use their arms when swinging the golf club, which tends to make the club head travel on a far side away from the body. In other words, the club head passes outside of the swing plane and because of this, the ball tends to get a clockwise spin (when the player is right-handed) at the time of impact. Such being the situation, there is proposed a practice device which allows the player to check his swing path.
For example, Patent Document 1 discloses a practice golf club which includes a club head attached with a bar member provided with a luminescent body, so that the swing path can be checked by watching a path of light from the luminescent body around the point of impact when the club is swung.
Also, Patent Document 2 discloses a practice device which includes a cord-like member having its one end detachably attached to a club head and the other end disposed at a ball position when the player makes an address; and a detection member attached to the grip of a club as an indication of a simulated position of the swing plane. As the club head moves, the cord-like member draw a path, which is detected by the detection member, so that a player can check his swing path.
Further, there are known simpler practice methods for mastering a proper swing path without using such dedicated devices as described above. An example is attaching a weight to the club head and another example is using two clubs, for repeated practice of a swing. These methods are based on a fact that a heavy golf club is difficult to swing with the arms alone and therefore can naturally lead the player to an integral use of his arms and body which is essential in an ideal swing action. The player may not be aware particularly of the swing plane, yet he is able to make his swing path closer to a proper swing plane. Therefore, it is possible to expect that a proper swing path will be learned by practice in repeating a swing by using such a method as described above.    Patent Document 1: JP-A Hei 10-5381    Patent Document 2: JP-A 2002-253721